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Fluid-Structure Interaction (FSI) using COMSOL Multiphysics

Today we have the pleasure of welcoming Nagi Elabbasi of Veryst Engineering as a guest blogger. Read on to see what this COMSOL Certified Consultant has to say about fluid-structure interaction.

Two weeks ago I led a webinar on fluid-structure interaction (FSI) using COMSOL Multiphysics. FSI involves coupling between a deformable or moving structure and a surrounding or internal fluid flow. There is a growing number of engineering and scientific problems where a purely structural or purely CFD analysis just aren’t accurate enough. Both analyses have to be accounted for simultaneously. Some examples are valve chatter, damping in MEMS, cardiovascular modeling, and shock absorbers.

The webinar highlighted the important features and capabilities available for FSI analysis in COMSOL Multiphysics, including the types of FSI coupling, the solution algorithms used, the available solvers, and the handling of the moving fluid mesh. COMSOL provides a wide range of capabilities for the advanced user, and also automates most of the steps required for FSI analysis, which is great for both novice and advanced users.

COMSOL offers two types of solvers for fluid-structure interaction problems (as well as other multiphysics problems). The first is the fully coupled solver, or monolithic solver as it is sometimes called in literature, and the second is the segregated solver (or partitioned solver). Having both solvers enables optimal solver selection for a wide range of FSI problems. The default solver settings work well for most problems, but there are also a lot of solver functionalities for advanced users to adjust for tougher problems. The fluid mesh movement algorithm can also handle severe mesh deformation, as shown below.

We also demonstrated how we at Veryst Engineering used COMSOL Multiphysics to set up two “non-standard” FSI problems and make engineering simplifications that significantly reduce solution times. In the case of a sea floor energy harvester, the solid part of the model was reduced to one degree of freedom (vane rotation), and in the case of the stretching of a fluid-filled hose, the enclosed fluid region was reduced to a single global constraint.

Peristaltic Pump Model

After the two non-standard FSI problems, we showed an interesting FSI example involving a 3D peristaltic pump. Peristaltic pumps move fluid by squeezing on a tube, causing the fluid inside to move. The deformation of the tube is strongly coupled to the fluid flow inside it, so an FSI analysis is required. The model is also nonlinear due to the large rotations of the roller, the nonlinear material response of the tubes, and the contact between the rollers and the tube. We were able to use this model to predict stresses in the tube and flow conditions, including flow fluctuations. The figure below shows the von Mises stresses in one tube configuration. You can find more details on this pump model in a paper we presented at the COMSOL Conference 2011.

Live FSI Demo using COMSOL Multiphysics

We also held a live demo, showing the important steps involved in setting up and running a fluid-structure interaction analysis in COMSOL. We set up a 2D simplified version of the peristaltic pump model that captures some of the flow characteristics of the full 3D model.

About the Guest Author

Nagi Elabbasi, PhD, is a Managing Engineer at Veryst Engineering LLC. Nagi’s primary area of expertise is modeling and simulation of multiphysics systems. He has extensive experience in finite element modeling of structural, CFD, heat transfer, and coupled systems, including fluid-structure interaction, conjugate heat transfer, and structural-acoustic coupling. Veryst Engineering provides services in product development, material testing and modeling, and failure analysis, and is a member of the COMSOL Certified Consultant program.